Methods and apparatus for alignment of ion beam systems using beam current sensors

Abstract

An ion beam is sensed with a beam current sensor which has a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the beam current sensor. The sensed ion beam current is indicative of ion beam position relative to a desired ion beam path. The ion beam position may be adjusted if the sensed ion beam position differs from the desired ion beam path. One or more beam current sensors may be utilized in an ion implanter for calibration and/or alignment. The beam current sensor may be utilized to determine a relation between a characteristic of an ion beam, such as magnetic rigidity, and a parameter of a system element, such as magnetic field, required to direct the ion beam along a desired ion beam path.

What is claimed is:  
     
       1. A method for sensing an ion beam, comprising the steps of: 
       generating an ion beam and directing the ion beam along a beamline; and  
       sensing the ion beam with a beam current sensor positioned on or adjacent to the beamline, said beam current sensor having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the beam current sensor, wherein the sensed ion beam current is indicative of ion beam position relative to a desired ion beam path.  
     
     
       2. A method as defined in  claim 1  further comprising the step of adjusting the ion beam position if the sensed ion beam position differs from the desired ion beam path. 
     
     
       3. A method as defined in  claim 2  wherein the step of adjusting the ion beam position comprises adjusting the ion beam position for maximum sensed ion beam current. 
     
     
       4. A method as defined in  claim 2  further comprising the step of applying a magnetic field to the ion beam, wherein the step of adjusting the ion beam position comprises adjusting the magnetic field applied to the ion beam. 
     
     
       5. A method as defined in  claim 4  further comprising the step of determining the magnetic field required to direct the ion beam along the desired ion beam path. 
     
     
       6. A method as defined in  claim 2  further comprising the step of applying an electric field to the ion beam, wherein the step of adjusting the ion beam position comprises adjusting the electric field applied to the ion beam. 
     
     
       7. A method as defined in  claim 2  wherein the ion beam is generated in an ion source having a movable electrode and wherein the step of adjusting the ion beam position comprises adjusting a position of the movable electrode. 
     
     
       8. A method as defined in  claim 1  wherein the step of sensing the ion beam comprises: 
       sensing the ion beam with a plurality of beam current sensors located at different positions on or adjacent to the beamline, each of said beam current sensors having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the respective current sensor, wherein the ion beam current sensed by each of said beam current sensors is indicative of ion beam position relative to the desired ion beam path.  
     
     
       9. A method as defined in  claim 1  wherein a system element changes the position of an ion beam with respect to the desired ion beam path depending on a parameter Y of the system element and a characteristic X of the ion beam, further comprising the step of determining, using the beam current sensor, a relation Y=f(X) between the characteristic X of the ion beam and the parameter Y of the system element that is required to direct the ion beam along the desired ion beam path. 
     
     
       10. A method as defined in  claim 9  wherein the characteristic X comprises the magnetic rigidity of the ion beam and wherein the parameter Y of the system element comprises the magnetic field produced by the system element. 
     
     
       11. A method as defined in  claim 9  wherein the characteristic X comprises the energy and the charge state of the ion beam and wherein the parameter Y of the system element comprises the electric field produced by the system element. 
     
     
       12. A method as defined in  claim 9  wherein the step of determining the relation Y=f(X) comprises measuring two or more sets of values of the characteristic X and the parameter Y required to direct the ion beam along the desired ion beam path. 
     
     
       13. A method as defined in  claim 9  wherein parameter Y is a linear function of the characteristic X and wherein the step of determining the relation Y=f(X) comprises measuring two sets of values (X 1 , Y 1 ) and (X 2 , Y 2 ) required to direct the ion beam along the desired ion beam path. 
     
     
       14. A method as defined in  claim 9  wherein the relation Y=f(X) is polynomial of order n and wherein the step of determining the relation Y=f(X) comprises measuring n+1 sets of values (X n , Y n ) required to direct the ion beam along the desired ion beam path. 
     
     
       15. A method as defined in  claim 1  further comprising the steps of: 
       using the beam current sensor to determine a first magnetic field B 1  required to direct a first ion beam having a first magnetic rigidity R 1  along the desired ion beam path;  
       using the beam current sensor to determine a second magnetic field B 2  required to direct a second ion beam having a second magnetic rigidity R 2  along the desired ion beam path; and  
       from the values of B 1 , B 2 , R 1 , and R 2 , calculating values of a 0  and a 1  in the equation:  
       
         
           
             B=a 
             1 
             R+a 
             0  
           
         
       
       thereby providing a relation between magnetic rigidity R of an ion beam and magnetic field B. 
     
     
       16. A method as defined in  claim 15  wherein the steps of determining a first magnetic field B 1  and determining a second magnetic field B 2  each comprises the steps of: 
       generating an ion beam;  
       sensing the position of the ion beam with the beam current sensor;  
       adjusting the magnetic field applied to the ion beam until the beam current sensor indicates that the ion beam is directed along the desired path; and  
       recording the value of magnetic field required to direct the ion beam along the desired path.  
     
     
       17. A method as defined in  claim 16  wherein the step of adjusting the magnetic field includes adjusting the magnetic field for maximum sensed current. 
     
     
       18. A method as defined in  claim 1  further comprising the step of translating the beam current sensor relative to the ion beam in a direction transverse to the ion beam, wherein the sensed ion beam current is indicative of ion beam size in the transverse direction. 
     
     
       19. A method as defined in  claim 18  wherein the step of translating the beam current sensor relative to the ion beam comprises translating the beam current sensor relative to a fixed ion beam. 
     
     
       20. A method as defined in  claim 18  wherein the step of translating the beam current sensor relative to the ion beam comprises deflecting the ion beam relative to a fixed beam current sensor. 
     
     
       21. An ion implanter comprising: 
       an ion source for generating an ion beam and for directing the ion beam along a beamline toward a target position;  
       an ion beam deflection element disposed along said beamline for deflecting said ion beam relative to said beamline;  
       a beam current sensor positioned on or adjacent to said beamline for sensing ion beam current, said beam current sensor having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at said current sensor, wherein the sensed ion beam current is indicative of ion beam position relative to a desired ion beam path; and  
       means for adjusting said ion beam deflection element, in response to the sensed ion beam position, so that said ion beam is directed along the desired ion beam path.  
     
     
       22. An ion implanter as defined in  claim 21  wherein said ion beam deflection element comprises a magnetic deflection element for applying a magnetic field to the ion beam and wherein said means for adjusting said ion beam deflection element comprises means for adjusting the magnetic field applied to the ion beam by said deflection element. 
     
     
       23. An ion implanter as defined in  claim 21  wherein said beam current sensor comprises a plurality of beam current sensors located at different positions on or adjacent to the beamline, each of said beam current sensors having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the respective current sensor, wherein the ion beam current sensed by each of said beam current sensors is indicative of ion beam position relative to the desired ion beam path. 
     
     
       24. An ion implanter as defined in  claim 21  wherein said ion beam deflection element changes the position of said ion beam with respect to the desired ion beam path depending on a parameter Y of the deflection element and a characteristic X of the ion beam, said apparatus further comprising means, using the beam current sensor, for determining a relation Y=f(X) between the characteristic X of the ion beam and the parameter Y of the deflection element that is required direct to the ion beam along the desired ion beam path. 
     
     
       25. An ion implanter as defined in  claim 24  wherein said deflection element comprises a magnetic element, wherein the characteristic X comprises the magnetic rigidity of the ion beam and wherein the parameter Y comprises the magnetic field produced by the magnetic element. 
     
     
       26. An ion implanter as defined in  claim 24  wherein said deflection element comprises an electrostatic element, wherein the characteristic X comprises the beam energy and charge state of the ion beam and wherein the parameter Y comprises the electric field produced by the electrostatic element. 
     
     
       27. An ion implanter as defined in  claim 21  further comprising: 
       means for using the beam current sensor to determine a first magnetic field B 1  required to direct a first ion beam having a first magnetic rigidity R 1  along the desired ion beam path;  
       means for using the beam current sensor to determine a second magnetic field B 2  required to direct a second ion beam having a second magnetic rigidity R 2  along the desired ion beam path; and  
       means for calculating values of a 0  and a 1  from the values B 1 , B 2 , R 1 , and R 2  in the equation:  
       
         
           
             B=a 
             1 
             R+a 
             0  
           
         
       
       thereby providing a relation between magnetic rigidity R of an ion beam and magnetic field B for the ion implanter. 
     
     
       28. A method for determining a relation between magnetic rigidity R of an ion beam and magnetic field B required to direct the ion beam along a desired path in an ion implanter, comprising the steps of: 
       positioning a beam current sensor on or adjacent to the desired path, said beam current sensor having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the beam current sensor;  
       using the beam current sensor to determine a first magnetic field B 1  required to direct a first ion beam having a first magnetic rigidity R 1  along the desired path;  
       using the beam current sensor to determine a second magnetic field B 2  required to direct a second ion beam having a second magnetic rigidity R 2  along the desired path; and  
       from the values of B 1 , B 2 , R 1  and R 2 , calculating values of a 0  and a 1  in the equation:  
       
         
           
             B=a 
             1 
             R+a 
             0  
           
         
       
       thereby providing a relation between magnetic rigidity R of an ion beam and magnetic field B for the ion implanter. 
     
     
       29. In an ion beam system wherein a system element changes the position of an ion beam with respect to an ion beam path depending on a parameter Y of the system element and a characteristic X of the ion beam, a method for calibrating the system element comprising the steps of: 
       positioning a beam current sensor on or adjacent to the ion beam path, said beam current sensor having a sensing aperture that is smaller than a cross-sectional dimension of the ion beam at the beam current sensor; and  
       using the beam current sensor, determining a relation Y=f(X) between the characteristic X of the ion beam and the parameter Y of the system element that is required to direct the ion beam along the ion beam path.  
     
     
       30. A method as defined in  claim 29  wherein the characteristic X comprises the magnetic rigidity of the ion beam and wherein the parameter Y comprises the magnetic field produced by the system element. 
     
     
       31. A method as defined in  claim 29  wherein the characteristic X comprises the energy and the charge state of the ion beam and wherein the parameter Y comprises the electric field produced by the system element. 
     
     
       32. A method as defined in  claim 29  wherein the step of determining the relation Y=f(X) comprises the step of measuring two or more sets of values of the characteristic X and the parameter Y required to direct the ion beam along the desired ion beam path. 
     
     
       33. A method as defined in  claim 29  wherein parameter Y is a linear function of the characteristic X and wherein the step of determining the relation Y=f(X) comprises measuring two sets of values (X 1 , Y 1 ) and (X 2 , Y 2 ) required to direct the ion beam along the desired ion beam path. 
     
     
       34. A method as defined in  claim 29  wherein the relation Y=f(X) is polynomial of order n and wherein the step of determining the relation Y=f(X) comprises the step of measuring n+1 sets of values (X n , Y n ) required to direct the ion beam along the desired ion beam path.